Pleural mesothelioma is a form of cancer that develops in the pleura, or outer lining of the lungs. The mesothelium is a large membrane of tissue that provides a protective surface for several of the body's organs and for both the chest cavity and the abdominal cavity. Pleura is a term for the dual layered mesothelium membrane that surrounds the lungs; the outer layer (the parietal layer) attaches to the chest wall, while the inner layer (the visceral layer) wraps around the lungs. The narrow space between the two is called the pleural area. This particular form of malignant mesothelioma is by far the most common, constituting up to seventy percent of all diagnosed cases of mesothelioma.
The only known cause of mesothelioma is asbestos; specifically, microscopic fibers that find their way into the human body. The most common method for human absorption of asbestos fibers is inhalation, generally inhalation of fibers given off by deteriorating or mangled asbestos products. When these fibers are inhaled the body is incapable of shedding them through any physiological process. The fibers lodge in the lungs and in many cases, work their way through the lungs over time to embed themselves in the pleura, the outer lining of the lungs.
Impact of Asbestos Fibers on the Pleura
These fibers will cause changes to the mesothelium cells that form the pleural membrane over a long period of time. Eventually the cells will begin uncontrolled growth - thickening the pleural walls, causing a buildup of fluid, and eventually leading to the development of mesothelioma cancer in the form of tumors. Often this process can take twenty years or more, which is why mesothelioma is usually diagnosed long after the exposure to asbestos has occurred. Asbestos fibers slowly cause things to go awry in the pleural space, causing a number of symptomatic developments.
As swelling begins to occur in the mesothelium, the space between the outer lung and the chest wall begins to narrow. Normally there is a thin layer of fluid that allows these two surfaces to slide against one another. When the swelling causes the fluid to dissipate, a dry rubbing of the chest wall and the lung surface can occur with every breath, causing acute discomfort.
Developing mesothelioma can also have the opposite effect in the pleural space by causing the development of excess fluid in the area. This condition is a common mesothelioma symptom and is called pleural effusion. Excess fluid in the chest cavity reduces the ability to draw a full breath. One of the early non-surgical treatments for this symptom is drainage of the excess fluid in order to lessen the patient's discomfort. This condition eventually develops in 80% to 95% of all pleural mesothelioma cases; in 60% of those cases it develops on the right side of the chest cavity.
The continued presence of asbestos fibers in the pleural mesothelium can occasionally trigger the development of nodes that sometimes calcify on both the lung lining and the parietal layer lining the chest wall. These nodules are called pleural plaques. They can be indicative of fibrosis in the lungs, leading to the development of asbestosis. They can also be a precursor to the development of malignant mesothelioma cells. Some patients are fortunate and develop pleural plaques without the development of an active disease. In all cases however pleural plaques are assumed to be associated with the presence of asbestos.
Pleural mesothelioma is a "diffuse" form of cancer, meaning that it usually consists of many small tumors spread over the mesothelium membrane, rather than a single large tumor. That makes the disease more difficult to treat with standard chemotherapy and radiologic therapy because there is no single mass to target. In recent years researchers have developed some methods of using chemical intervention to allow for precise targeting of malignant cells in this complex oncological environment.
Pleural Mesothelioma Symptoms
Mesothelioma symptoms can be misleading, as they resemble symptoms associated with more common afflictions such as asthma, allergies, cardiovascular problems, pneumonia and even tuberculosis. Because of a twenty to forty year latency period for the disease, mesothelioma patients are generally in their sixties or older and often may be expected to be exhibiting respiratory difficulties that come with age and, perhaps, smoking. There is an inherent irony in the fact that the disease is sufficiently rare that it is often not considered by diagnosing physicians until other possibilities are eliminated. Nevertheless because asbestos was so pervasive in the mid twentieth century tens of thousands of American workers have developed it and often died without a proper diagnosis.
Some of the common symptoms for pleural mesothelioma:
- A persistent cough that is harsh and dry
- Shortness of breath
- Painful inhalation
- Chest pain
- Weight loss
- Fever or night sweats
- Persistent fatigue
Often the type of chest pain associated with either "wet" or "dry" pleural effusion help to differentiate from pain associated with cardiovascular problems or with more common respiratory ailments. Pain in the anterior chest wall associated with difficulty inhaling is characteristic of pleural effusion combined with cancerous invasion of the tissue lining the chest wall, the parietal pleura.
Pleural Mesothelioma Diagnosis
Diagnosis procedures for chest-related symptoms often begin with a chest X-ray. These images may show the thickening of the pleural wall, an initial indication of cell malfunction in the pleural membrane. An MRI or CT scan may confirm the presence of fluid in the pleural area, which can be taken as a primary indicator of mesothelioma.
The search for malignant cells often begins with extraction of some of the excess fluid in the pleural area. Often this procedure is accompanied by a biopsy that extracts a small tissue sample from the pleural mesothelium. In recent years, Australian researchers have discovered a protein "marker' associated with the presence of malignant pleural mesothelioma that has proven to be present in 84% of the clinical test cases. That marker can be found with a simple blood test.
Treatment for Pleural Mesothelioma
Unfortunately, pleural mesothelioma is usually diagnosed only after it has been active in the body for a long period, giving mesothelioma patients a low probability of receiving a good pleural mesothelioma prognosis. The disease is always fatal; the question is how long the patient's life after diagnosis can be prolonged. One of the most important benchmarks for reasonably successful treatment is "respectability." If the cancerous tissue is sufficiently contained that it can be removed surgically, the survival period can be extended substantially. Often this type of surgery includes removal of a lung lobe in order to insure against the cancer spreading through the lung. With or without surgery, treatment usually includes both chemotherapy and radiotherapy.
There has been a good deal of research on mesothelioma treatment, with the specific goal of extending the life expectancy for victims of the disease. While the disease can be slowed, it cannot be stopped. Today, the use of new medications in chemotherapy and with the use of radiation treatment during surgery life expectancy is being extended slowly, with small steps.
- Agency for Toxic Substances and Disease Registry Asbestos Health Facts, http://www.atsdr.cdc.gov/asbestos/asbestos/health_effects/
- Malignant Pleural Mesothelioma: a Comprehensive Review - Moffitt Cancer Center Division of Thoracic Oncology, 2006, http://www.moffitt.org/CCJRoot/v13n4/pdf/255.pdf
- Chest Journal, American College of Chest Physicians, 1971
- Moffitt, p.4
- Targeted Drug Delivery to Mesothelioma Cells Molecular Cancer Therapeutics November 2007